Method of cleaning ovens

ABSTRACT

AN OVEN WALL CLEANING COMPOSITION HAVING AS THE ACTIVE CLEANING AGENT AN OXIDIZING SALT SUCH AS SODIUM NITRATE, OR OTHER ALKALI METAL OR ALKALINE EARTH METAL, NITRATE, IN COMBINATION WITH A SUFFICIENT AMOUNT OF A CAUSTIC ALKALI, SUCH AS SODIUM HYDROXIDE TO GIVE THE MIXTURE AN ALKALINE REACTION. SUCH MIXTURES ARE APPLIED TO AN OVEN WALL SURFACE THAT HAS BECOME GLAZED WITH HEAT-PRODUCED FATTY RESIDUES, AND CLEANING IS EFFECTED BY HEATING THE TREATED SURFACE T O A SUFFICIENTLY HIGH TEMPERATURE ABOVE ABOUT 230*C., FOR A PERIOD OF TIME SUFFICIENT TO BURNS OFF THE FATTY RESIDUES AND LEAVES THE SURFACE SUBSTANTIALLY CLEAN. THE CLEANNG COMPOSITION CAN BE APPLIED DRY TO A LOWER HORIZONTAL SURFACE OR CAN BE DISPERSED IN A CARRIER, SUCH AS AN AQUEOUS VEHICLE IN THE FORM OF A SATURATED SOLUTION, SLURRY, GEL OR THE LIKE, WITH OR WITHOUT A SURFACTANT, AND APPLIED BY BRUSHING, SPRAYING, WIPING OR RUBBING ONTO THE OTHER OVEN WALL SURFACES.

US. Cl. 134-2 3 Claims ABSTRACT OF THE DISCLOSURE An oven wall cleaningcomposition having as the active cleaning agent an oxidizing salt suchas sodium nitrate, or other alkali metal or alkaline earth metal,nitrate, in combination with a sufiicient amount of a caustic alkali,such as sodium hydroxide to give the mixture an alkaline reaction. Suchmixtures are applied to an oven wall surface that has become glazed withheat-produced fatty residues, and cleaning is effected by heating thetreated surface to a sufiiciently high temperature, above about 230 C.,for a period of time sufiicient to burn off the fatty residues and leavethe surface substantially clean. The cleaning composition can be applieddry to a lower horizontal surface or can be dispersed in a carrier, suchas an aqueous vehicle in the form of a saturated solution, slurry, gelor the like, with or without a surfactant, and applied by brushing,spraying, wiping or rubbing onto the other oven wall surfaces.

SUMMARY OF THE INVENTION The method of my invention comprises applying acleaning composition to a metal or other wall surface of home orindustrial ovens exposed to the spattering of fats and greases, or otheroily substances, and having thereon a heat-produced glaze, film, stainor the like, containing residues from oily substances of vegetable,animal or mineral origin. The method of cleaning is especiallyapplicable to walls of home and industrial ovens formed of aluminum orother metal, whether bare or coated, as with porcelain enamel. Duringuse in cooking, such oven walls are coated over with a glaze ofheat-produced residues, which adhere tightly to the interior oven wallsto form an unsightly stained coating or film, herein generally referredto as a glaze.

In some of the more modern electrically heated ovens, the glaze can beburned off by raising the temperature of the oven walls sufficientlyhigh, in the neighborhood of 700 to 800 F., to burn off the glaze andleave the wall surfaces substantially clean and of their original color.The burn-off can be satisfactorily carried out without the previousapplication of any cleaning composition, but a large amount ofelectricity or gas is consumed in heating up the oven walls to such hightemperatures.

The present method is carried out at a substantially lower temperaturewithin the range of about 230 C. to 290 C.

My cleaning composition contains as the active cleaning agent a mixtureof an oxidizing salt selected from the group consisting of alkali metaland alkaline earth metal nitrates and caustic alkali, such as causticsoda, in an mount sufficient to impart to the mixture an alkalinereaction.

The selected mixture of a nitrate and caustic alkali can be applied dry,powdered, or in granular form, or dispersed in a suitable aqueousvehicle for application by spraying, brushing, wiping or rubbing ontothe glazecoated surface to be cleaned. The surface is then heated to asufficiently high temperature, within the range of from 230 to 290 C.,to burn-off the glaze and leave a clean surface behind. The termburn-off is used in the same sense that it is applied to the resultsobtained when United States Patent O 3,591,416 Patented July 6, 1971 thewalls of an electrically heated cooking oven are brought up to atemperature sufiiciently high to remove unwanted grease stains, coatingsand the like.

DETAILED DESCRIPTION OF THE INVENTION The oxidizing salt that I preferto use in the composition of my invention is sodium nitrate, but otheroxidizing salts such as other alkali metal and the alkaline earth metalnitrates can be used, together with a sufficient amount of an alkalinereacting compound, such as sodium hydroxide, to give the composition analkaline reaction. The following tests indicate that while sodiumhydroxide (NaOH) can be used by itself to effect the cleaning of glazedoven walls, it is too corrosive for satisfactory use, but when sodiumhydroxide is combined with an alkali metal or an alkaline earth metalnitrate, no corrosive effect results, even on an aluminum surface.

For purposes of simulating the conditions under which glazing of ovenwalls occurs, the following oven tests were carried out:

Grease alone A 30% solution of No. 2 grease was prepared by mixing 30grams of No. 2 grease with grams of isobutanol in a 250 ml. Erlenmeyerflask. Solution was brought about by Warming the resulting mixture on awarming plate.

Grease and oil Another 30% solution was prepared, this time by combining10 grams of No. 2 grease, 20 grams of MC800 oil and 70 grams ofisobutanol in a 250 ml. 'Erlenmeyer flask. Solution was again broughtabout by warming.

Simulated oven tests Tests were made using metal plates each havingsixteen depressions, or dimples, therein for receiving the grease andgrease plus oil solutions. In each case, 0.4 m1.

of the respective solutions were placed in each of the respective setsof 16 depressions. The test plates were then placed in an oven at 280 to285 C. for 1 hour 45 minutes each. This resulted in a black crust beingformed in each depression, whether containing the solution of greasealone or the solution of grease and oil.

In the next step, a solution of sodium nitrate alone was prepared bydissolving 15.7 grams of sodium nitrate in water and diluting theresulting solution to 900 ml. in a column with distilled water. Thesodium nitrate plus sodium hydroxide solution was made by combining 3.1grams of sodium hydroxide and 12.6 grams of sodium nitrate and dilutingto ml. to give a total of 15.7 grams of material dissolved in theresulting solution. Thus, both of the solutions prepared contained0.0157 gram of material in each 0.1 ml. of solution.

The plates were then treated with the respective materials, the amountof material added to each depression being 1.4 ml. or 0.22 gram in eachcase.

After being allowed to stand overnight, or other effective equivalentsoaking period the respective grease and grease plus oil plates wereplaced in an oven at 280 C. and removed 2 /2 hours later for evaluation,the temperature of the oven being maintained at 280 C. plus or minus 5C.

The thus treated test plates were then placed back in the oven at 280285C. and kept at that temperature for at least one hour and preferablyabout 2 hours before removal. After removal of the test plates, theplates were allowed to cool and then rinsed with tap water. Theevaluation was then made on the percent of clean metal area aftertreatment, based upon the total area treated. A tabulation of theresults obtained is as follows:

TAB LE NO. 1

Percent of clean Treating material (salt surface area after Plate withbaked on or salt plus caustic) treatment Grease N Do N From theforegoing tabulation of results it will be evident that while sodiumnitrate alone shows a removal of and 70%, respectively, for grease andgrease plus oil, the combination of sodium nitrate with sodium hydroxidegives better results, 30 and 90% removal, respectively, with greasealone and with grease plus oil. The higher percent of removal of theburned-on grease, or grease plus oil, residues is believed to be due tothe resulting alkalinity of sodium nitrate-caustic soda mixture, butcaustic soda alone results in excessive corrosion of the metal plate.

Another set of tests was run, using a stainless steel plate 7%" square,containing 16 circular depressions, each 1 /2" in diameter and A2" indepth. Similar conditions were used as above described, except that adrop of a non-ionic surfactant, Triton X-100 (isooctyl phenylpolyethoxyethanol containing 9-10 ethyleneoxide groups per molecule),was placed in each depression over the glaze before adding the treatingsolution of NaNO or of NaNO plus NaOH in the total amount of 0.22 gram,as before in the proportions of NaNO to NaOH designated below:

Where two figures for Percent Removal are given, they representdifferent tests.

As indicated in Table No. 2, the combination NaNO and from 1 to 40% ofNaOH by weight of the total performed well in the removal of baked ofbaked-on grease, which was somewhat more difiicult to remove than wasthe baked-on grease plus oil. The amount of corrosion was directlyproportional to the percentage of NaOH, and above the 50% level of NaOHsome corrosion was noticed. The greatest amount of corrosion wasexhibited by a solution of NaOH alone, where a 90% and a 98% removal inthe case of grease and grease plus oil, respectively, were observed.

Satisfactory results can thus be obtained by using from 1 to 40% ofcaustic soda (NaOH) by weight of the mixture of sodium nitrate andsodium hydroxide. In place of sodium nitrate, other alkali metalnitrates or alkaline earth metal nitrates and equivalent proportions ofsodium hydroxide can be used with satisfactory results if at least 0.01gram/cm. and preferably 0.02 gram/cm. of the composition is spread overthe glazed oven surface.

Accordingly, the composition of my invention preferably utilizes sodiumnitrate, together with a sufficient amount of sodium hydroxide to renderthe mixture alkaline. More broadly stated, however, my inventioncomprises the use of any alkali metal or alkaline earth metal nitrate incombination with a sufficient quantity of an alkali metal or alkalineearth metal hydroxide to give the mixture an alkaline reaction.

It will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention.

I claim:

1. The method of cleaning a metal surface having thereon a heat-producedglaze of fatty residues, the steps which comprise spreading over saidglazed metal surface so as to adhere thereto an aqueous compositionconsisting essentially of a salt selected from the group consisting ofalkali metal nitrates and alkaline earth metal nitrates and mixturesthereof, and an alkali metal hydroxide in an amount sufficient to impartto said composition an alkaline reaction, and

after allowing said composition to remain spread over said surface foran effective soaking period heating said glazed metal surface with saidcomposition adhering thereto to a sufficiently high temperature between230 C. and 290 C. for a sufficient length of time to remove said glazeand leave said surface substantially clean.

2; The method as defined by claim 1, wherein the metal surface is analuminum surface.

3. The method as defined by claim 2, wherein the aluminum surface is theinterior surface of a cooking oven, and said glazed metal surface isheated to at least a temperature of about 280 C. for at least about onehour.

References Cited UNITED STATES PATENTS 2,357,970 9/1944 Rath 134-2X2,674,548 4/1954 Balz 1342 2,674,549 4/ 1954 Balz 134-2 3,046,165 7/1962Halversen et al. 134-2X 3,085,035 4/1963 Ireland ct al. 1342X 3,375,1553/1968 Adams 134--2X 3,425,947 2/ 1969 Rausch et al. 134--39X MORRIS O.WOLK, Primary Examiner J. T. ZATARGA, Assistant Examiner US. Cl. X.R.134-19, 22, 39, 40

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,591,416 Dated H1116, 1971 Inventor(s) Carl E. Johnson It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 52, cancel "of baked" (first occurrence);

Same column, line 56, change "50" to --5-.

Signed and sealed this 1 1th day of July 1972.

(SEAL) Attest:

EDWARD M'.FLETCHER,JR. ROBERT GOTISCHALK Attesting Officer Commissionerof Patents FORM powso 7 USCOMM-DC wan-poo UTS. GOVERNMENT PIINTlNGOFFICE HUD 0-366-3.

